1. Field of the Invention
The present invention relates to a positive resist composition, especially to a positive resist composition using a polymer compound suitable as a base resin for a chemically amplifying positive resist composition, and to a patterning process using the same.
2. Description of the Related Art
As LSI advances toward higher integration and processing speed, miniaturization of the pattern rule is progressing rapidly. Especially expansion of the flash memory market and increase in the memory capacity lead this miniaturization. The 65-nm node device is being mass-produced by an ArF lithography as the cutting-edge technology for miniaturization; and mass-production of the 45-nm node by an ArF immersion lithography as the next generation technology is under preparation. Candidate for the next generation 32-nm node that is being under investigation includes; the immersion lithography by a super high NA lens formed of a combination of a liquid having a higher refractive index than water, a lens having a high refractive index, and a resist film having a high refractive index; a lithography by a vacuum ultraviolet (EUV) of the wavelength of 13.5 nm; and a double exposure of an ArF lithography (double patterning lithography).
In high energy beams of extremely short wavelengths such as EB and X-ray, a light element such as hydrocarbon that is used in a resist composition hardly shows absorbance, so that a resist composition based on polyhydroxy styrene is being under investigation.
As to the exposure instrument for mask production, in order to enhance line-width precision, the exposure instrument using an electron beam (EB) has been used from the exposure instrument using a laser beam. Moreover, by increasing the acceleration voltage of an electron beam gun, further miniaturization becomes possible; and thus, the acceleration voltage has been increased from 10 kV to 30 kV, with the recent main stream thereof being 50 kV, and further study of even 100 kV is currently taking place.
Note that, deterioration in sensitivity of the resist film is becoming a problem as the acceleration voltage is increased. As the acceleration voltage is increased, the forward scattering effect within the resist film becomes smaller so that contrast of the electron beam drawing energy is enhanced thereby leading to improvement in resolution and size controllability, while sensitivity of the resist film is deteriorated because the electron passes through the resist film with free draining condition. In the mask exposure instrument, direct drawing is done by way of the one-stroke sketch so that deterioration in sensitivity of the resist film causes decrease in the productivity; and thus, this is not desirable. Accordingly, because of the request for higher sensitivity, investigation of a chemically amplifying resist composition is getting underway.
Simultaneously with miniaturization of the pattern of the EB lithography for mask production, thinning of the resist is progressing in order to prevent pattern fall during development due to a high aspect ratio. In the photolithography, thinning of the resist contributes significantly to enhancement of the resolution. This is because a device became more flattened by introduction of CMP and others. In mask production, a substrate is flat so that film thickness of the substrate to be processed (such as for example, Cr, MoSi, and SiO2) has been determined based on the light shielding rate and the phase difference control. To make the film thinner, the dry etching resistance of the resist needs to be enhanced.
Generally, it is said that there is a relationship between the resist carbon density and the dry etching resistance. In the EB drawing which is not influenced by absorption, the resist based on a novolak polymer having a high etching resistance has been developed.
To enhance the etching resistance, a styrene copolymer was firstly shown, and then, an indene copolymer and an acenaphthylene copolymer were shown in Patent Document 1 and in Patent Document 2, respectively, in which attempts were made to enhance the etching resistance by utilizing not only the high carbon density but also the rigid main chain structures due to these cycloolefin structures.
In Patent Document 3, a proposal was made to enhance the etching resistance by blending an existing resist compound with a compound having yttrium, aluminum, iron, titanium, zirconium, or hafnium; and as the iron-containing compound, ferrocene compounds such as ferrocene aldehyde, ferrocene methanol, ferrocene ethanol, ferrocene carboxylic acid, and ferrocene dicarboxylic acid were mentioned.